1. Field of the Invention
The field of the invention relates generally to engine control methodology for efficient engine operation.
2. Background of the Invention
The inventors herein have developed an engine control methodology that allows efficient engine operation with some of the cylinders operating with substantially no injected fuel and others combusting, for example, a lean air-fuel mixture. This allows the engine to operate at a higher engine load, thereby extending the lean limit of the combusting cylinders.
However, the inventors have also recognized that such operation is only desired in certain operating modes. In other operating modes, other conditions may be required, such as operating all of the cylinders near stoichiometry, or lean of stoichiometry.
As such, the inventors herein have developed a method for transitioning into and out of the mode with some cylinders having substantially no injected fuel and others operating to combust an air-fuel mixture. In one example, a method is provided for controlling an engine having a first and second group of cylinders. The method comprises (i) operating the engine in a first mode with the first group of cylinders combusting a lean mixture of air and injected fuel at a first ignition timing and the second group of cylinders having substantially no injected fuel, (ii) determining a request to operate in a second mode and, in response to said request, (iii) commencing fuel injection in the second group, and (iv) performing at least one of the actions selected from the group consisting of: retarding the first ignition timing of the first cylinder group, and decreasing airflow through the engine.